Complexes of neptunium

A significant amount of structural information has been gathered on neptunium complexes. For the main, they resemble corresponding U and Pu complexes. However, an EXAFS study of alkaline solutions of Np found evidence for a trans dioxo ion of the type P4p02(OH)4(OH2)]i-. 

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In summary, the solubility and sorption reactions of cobalt, strontium, neptunium, plutonium, and americium were found to be dependent on HLW compositions. Evidence revealed the formation in HLW of organic complexes of cobalt, strontium, and americium, and of hydroxide complexes of neptunium(V) and plutonium(V). Sorption reactions were dependent on radioelement complex formation and suspected waste/sediment reactions. These data can aid in assessing effects of future HLW processing operations as well as in judging the feasibility of continued storage of HLW in existing tanks. 

Kim J. I. and Sekine T. (1991) Complexation of neptunium(V) with humic-acid. Radiochim. Acta 55(4), 187-192. 

Rao L. and Choppin G. R. (1995) Thermodynamic study of the complexation of neptunium(V) with humic acids. Radiochim. Acta 69(2), 87-95. 

Attempts to make the octamethylplutonocene derivative by addition of tetramethyl[8]annulene dianion to the tetrachloride resulted in the reduction of Pu(IV) by the tetramethyl[8]annulene dianion to Pu(III).i When the borohydride complexes of neptunium and plutonium are used in place of the halide salts acceptable yields of the bis(tetra-roethyl[8]annulene) complexes were obtained.21... 

Rees TF, Daniel SR (1984) Complexation of neptunium(V) by salicylate, phthalate and citrate ligands in a pH 7.5 phosphate buffered system. Polyhedron 3 667-673... 

Because of the ease of oxidation of protactinium(IV) and uranium(IV), peroxides and peroxo complexes are limited to their higher oxidation states. The compounds M04"JcH20 precipitated from dilute acid solutions of neptunium(IV) and plutonium(IV) by hydrogen peroxide appear to be actinide(IV) compounds. Soluble intermediates of the type [Pu( U-02)2Pu]4+ are formed at low hydrogen peroxide concentrations. 

The formation of complex compounds of neptunium with cupferron and a number of other complexing agents has been studied.95 More recently, the extraction of neptunium(IV and VI) from HC1, HBr and HN03 media has been investigated.96... 

The presence of either HEDTA or EDTA resulted in significantly lower neptunium and plutonium sorption. Complexation of the neptunium and plutonium by HEDTA and EDTA may have caused the reduced sorption. However, this evidence for complex formation was not consistent with the observations made in the solubility studies (HEDTA increased and EDTA decreased neptunium solubility neither affected plutonium solubility). Thus, HEDTA and EDTA may have decreased neptunium and plutonium sorption through some undetermined effect on the sediment minerals. 

The vast majority of the studies reported have concerned the metals thorium and uranium, particularly the latter, due to accessibility of raw materials, ease of handling, and the long lifetimes of the relatively weakly a-emitting elements Th and U. In many cases, compounds of neptunium and plutonium with similar formulae to U and Th analogues have been made and found to be isomorphous and thus presumably isostructural. This chapter will therefore commence with, and concentrate largely on, the chemistry of complexes of these elements, followed by sections on the other actinides. 

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